Sensors which are used in wheel bearings are required, in particular, to measure the rotational speeds and the rotational behavior of the wheels of a motor vehicle, the vehicle containing a control system which processes this information as input variables for the control system. Such control systems are used, for example, for antilock control, traction control, driving stability control and the like. In this context, it is advantageous to measure direct measured variables. The measured variables include braking acceleration values, drive acceleration values, the rotational speed of the wheels, the angular acceleration and also values of lateral acceleration acting on the vehicle chassis. Because of the transmission of force from the roadway to the vehicle chassis, the wheel bearing is an optimum measuring point for sensing forces and accelerations.
Wheel bearings with sensors are already known in various embodiments. In this context, the sensor is arranged on and attached to the wheel bearing in different ways. In a wheel bearing sensor arrangement as per DE 195 32 328 A1, a sensor body is inserted into a receptacle opening in an attachment clip which is directly connected to the fixed part of the axle body, specifically to the wheel bearing outer ring, and is locked with a clamp.
DE 197 35 978 A1 discloses a wheel bearing in which the sensor is arranged in a depression in the wheel carrier which is open to a pulse transmitter. In this context, the sensor end face bears against a bearing part and is pressed against this bearing part by a spring which is arranged at the bottom of the depression.
Furthermore, DE 103 38 959 A1 discloses an arrangement of a sensor on a wheel bearing unit in which the sensor is attached to an outer wheel bearing ring of the wheel bearing unit and at the same time lies opposite an encoder which is rotationally movable with respect to the sensor, about a rotational axis of the wheel bearing unit. The wheel bearing unit has at least one row of roller bodies and a second row of roller bodies which is adjacent to the first row in the axial direction of the rotational axis, in which case the wheel bearing ring engages around at least one of the rows. The sensor is integrated into a housing and is attached to the outer bearing ring by means of a lever. The lever protrudes axially from the sensor and extends partially radially over the outer bearing ring. A bolt, which is partially pressed in, screwed in or fixed in some other way, holds the sensor against the outer bearing ring by means of the lever. The encoder is concealed with respect to the sensor by means of a covering plate. As a result, the encoder is admittedly protected against soiling and corrosion creep, but the bearing face of the sensor is not.
A disadvantage with these known devices is the relatively complex means of attaching the sensor to the wheel bearing, in particular by providing additional components such as clamps, springs, levers etc.
Furthermore, the uniform distance which is to be maintained between the sensor and the encoder, encoder ring or pulse wheel, that is to say the sensor face and the encoder face to be detected, is an important feature for the operation of the measuring device on the wheel bearing and the associated control system. Corrosion creep on the attachment face of the sensor, in particular in its attachment region, which cannot be ruled out, constitutes a problem which should not be underestimated here. Corrosion creep, caused by moisture, on the attachment face of the sensor can lead to the sensor being pressed away from the encoder in the axial or radial direction as a function of its installation position, with the result that the distance between the sensor face and the encoder face is increased. This frequently leads to signal loss in the sensor, so that a reliable measurement of the rotational speed or rotational angle at the wheel bearing is adversely affected.